Electrical testing system



March 19, 192 P. e. EAR$ m. K7 ELECTRICAL-TESTING isi'sw Filed May 5, gze

INVENTORS W TTORNE Y Patented Mar. 19, 19219;

UNITED STATES mesa-1 PATENT OFFICE.

PAUL c. EDWARDS, E BnookLYm NE'w YORK, Ann nnnomi'w. HERBINGTON, or UPPER monrornm, NEW JERSEY, ASSIGNORS 'ro nME IcAN TELEPHONE AND TEL GEArH comrnnr', A. oonroan'rron on NEW YORK.

ELECTRICAL TESTING SYSTW.

Application filed May 5, 1926. Serial No. 106,993.

This invention relates generally to electrical testing systems, and particularly to sys- -te1ns"for the determination and measurement of the electrical characteristics of circuits 5 and apparatus. i J An object of the invention is to provide a simple system for determining separately and independently the react ance and resistance components of any impedance.

In this invention there is employed a Wheatstone bridge having known and unknown elements, and a current detecting device such as a galvanometer, having a fixed coil and a movable coil, these being arranged so as to measure anddetermine the charac:

ter1st1cs of the unknown elements. vThe movable coil of the current detecting device is adapted to be-energized when there is an unbalanced condition in the bridge so that an indication is made of this unbalanced condition. The movable coil is supplied with alternating current which is alternately inphase or in quadrature with the current supplied to one diagonal of'the Wheatstone bridge, and the fixed coil is energized by current hav-' ing a predetermined phase relationship with the currents supplied to the diagonal of the bridge. The bridge is supplied from a source having output brushes so arranged as to transmit currents to the bridge in quadrature with each other. A switch is included in the circuit for connecting one or another pair'of output brushes; to the bridge. In this arrangement two or three trials are necessary to obtain a good balance. Each trial gives a closer approximation. By the'arrangements of this invention itis possible to balance quickly one arm of-the bridge against'another. By these' balances 40 the magnitudes of the components ofany impedance may be obtained. .7

Other objects and advantages of the invention will be better understood from the detailed description hereinafter following when readfin connection withthe accompanying drawing showing two embodiments of the invention, in which Figure 1 shows a rotatable commutator associated with a lVheatstone bridge having. a telephone line as one of its arms for determiningt-he reactance and resistance componentsof the telephone line, and Fig. 2 shows a modification of the invention in whichthe reactance and resistance components of any impedance may be determine Referring to Fig. 1 of the drawing, there is shown a l/Vheatstone bridge having a telephone line L as one arm thereof; another arm ance R, which will be separate from and independent of the balance of the resistance R in series with the capacity 0 against the telephone line L. 1 I

A current detecting device includes a movable coil M and a fixed coil-F, the movable coil M being connected in one diagonal of obtained with such a device. by reason ofthe reaction of one coil upon the other and will, therefore, indicate no current when either of the coils is unexcited, or when the currents through these coils are inquadrature. The,

fixed coil F is supplied with alternating current, as will be'shown hereafter. When the bridge'isbalanced there will be no flow of current through the movable coil M, and the current detecting device'will show that a balanced condition exists. However, there will be described herein arrangements for shifting the current flowing in the movable coil M from one phase to another phase 90 degrees away. By this shifting rneans it is possible to discriminate between a true balance, i. e., when there is an absence of current in the movablecoil M, and a false'balance, i. e., due

to currents in the movable coil M and the fixed 'coil F whose phase relationship approaches quardrature, since it is well known the bridge. As is well known, a reading is I that in a current detecting device of the type employed in this invention there is an indica'-- tion of a balanced condition when currents flowing through the respective "windings thereof are exactly 90 degrees apart.

The source of excitation for the bridge consists of a motor driven commutator K (motor not shown), which may be made to revolve at any desired speed, and which may therefore transmit current ofany frequency, preferably a low frequency. The potential for the bridge is obtained from a unidirectional source S which is connected through a protective resistance R, to the input brushes l3,

.and B of the commutator K. The commutator K has three pairs of output brushes, B

and B B and B B and 13,, respectively,

two pairs of these brushes, B and B B and B being in quadrature with each other. The latter pairs of brushes are wired to a diagonal of the bridge throughra double-pole, doublethrow switch W and a protective resistance R By means of the switch W it is possible to shift from one pair of output brushes, B

and B to another pair of output brushes, B and B these pairs of brushes being in quadrature, as stated above. The brushes B and B are so placed on the commutator K that for one position of the switch W the current fiowing through the fixed coil F of the current ly insensitive to changes in the resistance R current in the movable coil Consequently, in determining the capacity reactance of the telephone line L (which has a large reactance component and a comparatively small resistance component) the resistance R- may be at first shunted and an approximate balance will be, neverthless,,indicated by the current detecting device.

- After a preliminary adjustment has been made between resistance R and R the switch W is moved to connect the other pair of output brushes to the diagonal of the bridge.

Now, the current detecting device will be sensitive to'ehanges in the resistance R by virtue-.of the fact that current, through the fixed coil F is substantially in base with the current flowing in the movable coil M due to v any unbalance of resistance R By adjusting the resistance R a balanced condition is .again indicated on the current detecting device. The switch W is then moved to connect the pair of output brushes previously connected to the diagonalof the bridge and the resistance R isbalanced against the resistance R,'.'

havebeen shown in two particular embodi- This operation may continue for two or three trials, notwithstanding, however, that when the bridge is absolutely balanced the current detecting device will indicate it regardless of which pair of output brushes is connected to 4 the'diagonal of the bridge. In practice, not

A more than two or three trials will be necessary.

\Vhen a true balance is obtained the reactance component of the telephone lineL will bear the same ratio to the reactance of the condenser C that the resistance R, bears to the resistance R Also, the resistance componentof the telephone line L will bear the same ratio to the resistance R, that the resistcurrent detecting device.

ance R bears to the resistance R lln practice, when it is desired to determine the distance to a fault in a bad wire of a telephone line, the reactances of the bad wire and a good wire sometimes called its mate, are compared. If the length'of the good wire is known, the distance to the fault in the bad .wire may be readily calculated.

When it is necessary to energize the fixed coil F of the current detecting device with 75. current having a potential different from that supplied to the diagonal of the bridge, the arrangement of Fig. 2 may be employed. In the arrangement of Fig. 2 the resistance and reactance components of any impedance have been schematically shown by reference characters R and 0,. These components, R and C together form one arm of the Whcat stone bridge which is balanced by the arm of the Wheatstone bridge including resist ance R, and condenser C The potential for the bridge is obtained from a source 3,. which is connected through a resistance R to the input brushes 13., and B of a commutator K Two pairs of output brushes located 90 degrees apart are connected to the outer terminals of the switch W, these pairs including brushes B and 13, B and B respectively. On the same shaft with the commutator K is another commutator K,. The input brushes of this commutator are B and B which are connected to a source S through a protective resistance R,,. The output brushes B and B are connected to the fixed coil F of the This arrangement of commutators gives the same effect as if an alternating current were supplied to the fixed coil F having the same frequency as, but a different voltage from that supplied to the bridge. The shaft on which the commutators K and K revolve has means associated therewith for varying the angle that the output brushes, B and B ofthe dommutator K make with either pair of optput brushes of the commutator K,, for example, B and B Inasmuch asthe operationvof the arrangement-shown in Fig.

2 is similar to that alreadydescribed for Fig. 1, it need not here be repeated.

' While the arrangements of this invention pairs of output brushes in quadrature with a pair of each other, a galvanometer havin T the windmutually reactive windings, one 0 windings, one winding being excited by the,

ings of said galvanometer being in a diagonal of said bridge, means for supplying current to the other winding of said galvanometer which has-a predetermined phase angle with the current derived from either pair of the output brushes of said alternator, and means for connecting one pair of the output brushes of said alternator to the other diagonal of the bridge so that the resistance component of the telephone line may be determined and for connecting the other pair of output brushes thereto so that the reactance component may be determined. i

2. In a system for measuring the resist ance and reactance components of a telephone line, a l/Vheatstone bridge having the telephone line as one arm thereof, an alternator having two pairs of output brushes arranged so as to supply currents to one diagonal of the lVheatstone bridge in quadrature with each other, a galvanometer having a pair of mutually reactive windings, one of said windings being movable and being connected to the other diagonal of the bridge, the first winding being fixed and being connected to the alternator so as to be supplied with current having a predetermined phase angle with respect to the current derived from either pair of the output brushes of said alternator, and means for connecting either pair of output brushes of said alternator to the first-mentioned diagonal of the bridge so that the resistance and reactance components of the telephone line may be separately balanced.

3. In a system for separately balancing the resistance and reactance components of'a telephone line connected to one arm of a VVheatstone bridge, the combination of a galvanometer having two mutually reactive current fiowing in one diagonal of the bridge, a source of alternating current connected to the other diagonal of the bridge for supplying alternating current thereto and also current in quadrature therewith, and means 'for exciting the other winding of said galvanometer by current having a definite phase angle with the current supplied to the latter diagonal of the bridge.

4. In a system for separately balancing the resistance and reactance components of an electrical impedance connected so as to form one arm of an electrical bridge, the combination of a current ddtecting device having two mutually reactive windings, one of said windings being excited by the unbalanced current of the bridge, means for supplying alternating current to the'bridge, means for supplying current inquadrature with said alternating current, and means for supplying the other winding of said current detecting device with current having a predetermined phase relationship with the current supplied to said bridge. I

'5. nIn anelectrical' bridge having a telephone line in one arm thereof and a fixed caarm thereof, a source of alternating current of definite frequency, a source of current in quadrature'therewith, means for connecting either of said sources of current across the bridge in one diagonal, and a currentv detectpacity and a variable resistance in another ing device connected across the bridge in the other diagonal, and'means whereby the resistance and reactance components of said telephone'line may be independently determined. 4

.6. In an electrical bridge having a telephone line in one arm thereof and a fixed capacity and a variable resistance in another arm thereof, the combination of a current detecting device comprising two mutually reactive windings, one of which is'movable and the other stationary, an alternator having three pairs of output brushes, two pairs of which are in quadrature with each other, the third pair of brushes making predetermined angles with the other pairs of brushes and'being connected to the stationary winding of said current detecting device, the movable winding of said current detecting device being connected in one diagonal of thebridge, and means for connecting either pair of output brushes in quadrature with each other to the other diagonal of the-bridge'so that the resistance and reactance components ofsaid telephone line may be independently determined.

7. In a system cuit impedanceof a telephone line, the combination of a source of alternating. current, means for providing current in quadrature therewith, an indicating device comprising two current responsive elements which c0- operate o produce indications thereon, an

' adjustable. reactance, a fixed resistance, an

adjustable resistance, means for interconnecting said telephone line, the adjustable reactance, the fixed resistanceand the adjustable "resistance so that when alternating current is applied the resistance adjustment on said indicating device will become sensitive and the reactance adjustment insensitive, and when current in quadrature therewith is applied the reactance adjustment on said indicating device will become sensitive and the resistance adjustment lnsensitive.

8. In a system for measuring the open circuit reslstance and reactance components of a telephone line, the combination of a generfquadrature with said alternating current, an indicating device comprising two mutually reactive elements cooperating to produce indications thereon, an electrical bridge comprising" the telephone line as a first arm, a fixed resistance as a second arm, anadjustable resistance as a third arm, and an adjust: able resistance in series with a fixed capacity for measuring the open eir- 1( J0' ator of alternating current and current in as a fourth arm, the indicating device being connected across the bridge in one diagonal, the alternating current being supplied to the bridge in the other diagonal so that the adjustable resistance of the'third arm may be balanced against the fixed resistance of'the second arm, current in quadrature therewith being supplied to the bridge so that the adjustable' resistance in series with the fixed capacity of the fourth arm may be balanced against the telephone line of the first arm.

9.- In an electrical bridge havin a telephone line inone arm thereof, the combination of a commutator having two sets of output brushes thereon 90 apart, means for connecting either of said output brushes to the bridge in one diagonal, acurrent detect ing device connected across the bridge in the other diagonal, and means whereby the resistance and reactance components of said "telephone line may be separately determined.

.10. In a system for separately determining the reactance and resistance components of a telephone line, the combination of a Wheatstone bridge having the telephone line in one arm thereof, a generator for generating currents in quadrature with eachother and a current having a predetermined phase relationship With said currents in quadrature,'means for applying either of the currents in quad rature to one diagonal of the bridge, and a current detecting device having two mutually reactive windings, one winding of said current detecting device being connected to the other diagonal of thebridge, and the other winding of said current detecting device be:

ing supplied with the current having the predetermined phase relationship with the cur rents in quadrature- In testimony whereof, We have signed our names to this specification this 4th day of May, 1926. v

' PAUL G. EDWARDS. I

HAROLD W. HERRINGTON. 

